The effect of silica fume on the washout resistance of environmentally friendly underwater concrete with a high-volume of siliceous fly ash

Abstract

Concrete with a high-volume of siliceous fly ash has recently been widely applied as underwater concrete (UWC) in marine structures. This study investigated the effect of the content of silica fume (SF) and the source of fly ash (FA) on the washout resistance of high-volume fly ash concrete (HVFAC) mixes. Class F fly ash sourced from two different locations in India was used to prepare eight HVFAC mixes, which were stabilized using increasing SF contents of 0, 5, 10, and 15 wt%, respectively. The washout loss of these UWC mixes was determined using a special plunge test with a long acrylic washout tube and a perforated steel container. Moreover, other properties such as the slump, air content, strength, void content, water permeability and sorptivity, and drying shrinkage of the prepared mixes were also validated. An enhancement in slump and washout resistance of up to 19% and 11% were noticed when the UWC mixes were prepared using FA with a greater surface area. With an increase in the content of SF, there was also an increase in the loss of the workability and strength of the UWC mixes. Moreover, the washout resistance and durability of these mixes increased. This confirms that the inclusion of SF stabilized the HVFAC mixes against water environments by adsorbing more free water on their surfaces. The pozzolanic reaction and microstructure densification mechanisms also increased the stabilization of the HVFAC. Designing UWC using HVFAC mixes stabilized with SF is environmentally friendly, and the application of such concretes in underwater environments is simple and cost-effective.